Integrated circuits are interconnected networks of electrical components fabricated on a common foundation called a substrate. The electrical components are typically fabricated on a wafer of semiconductor material that serves as a substrate. Various fabrication techniques, such as layering, doping, masking, and etching, are used to build millions of resistors, transistors, and other electrical components on the wafer. The components are then wired together, or interconnected, to define a specific electrical circuit, such as a processor or a memory device.
There is a general desire to reduce the sizes of the various components in integrated circuit fabrication. Reducing size is generally accompanied by a reduction in cost, as more and more devices can be fabricated on a single substrate, and a reduction in power requirements, as less power is needed to switch smaller components. However, this size reduction does not come without a cost. As integrated circuit devices become smaller and smaller, resistance and current leakage between components become increasingly problematic.
Dynamic random access memory (DRAM) is one example of an integrated circuit device. DRAM typically utilizes a memory cell having a capacitor or other charge storage device to hold a charge indicative of a data value of that memory cell. As these capacitors become smaller, their ability to hold a sufficient charge to permit sensing of the data value, and to maintain that charge for some desired period, becomes more critical.
Ruthenium (Ru) is often utilized as a bottom electrode for capacitors while strontium titanium oxide (SrTiO3), sometimes referred to as strontium titanate or simply STO, is utilized for the dielectric of the capacitor. However, STO grown directly on ruthenium tends to oxidize the ruthenium to form a nonstoichiometric ruthenium oxide (RuOx). This ruthenium oxide interface between the ruthenium electrode and the STO dielectric is generally undesirable. The ruthenium oxide tends to have a high surface roughness, high stress (due to lattice mismatch), and a low work function or barrier height with the STO, which are all undesirable for the desired dielectric properties of the STO.
Others have suggested the use of strontium ruthenium oxide (SrRuO3), sometimes referred to as strontium ruthenate or simply SRO, as an interface between the ruthenate electrode and the STO dielectric. See, Effect of Sr-Ruthenate Seed Layer on Dielectric Properties of SrTiO3 Thin Films Prepared by Plasma-Enhanced Atomic Layer Deposition, Ji-Hoon Ahn et al., Journal of The Electrochemical Society, 155(10) G185-G188, 2008. Such an interface between a ruthenium conductor and the STO dielectric has been shown to improve the dielectric properties of the STO dielectric. However, continuing improvements are desirable.
For the reasons stated above, and for other reasons that will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for alternative structures and their processes in the formation of integrated circuit devices.